Is my CPU too slow for 100 Mbit/s?

In the past I had a 50 down / 10 up connection where I got full speed. Now I upgraded to 100 down / 40 up and when I use my Draytek Vigor 130 without pfSense I get good speed as well (91 down/31 up). But with pfSense running and the Modem in bridged mode I only get 50 down / 27 up. I disabled the Traffic Shaper and then I had 69 down / 32 up. I opened Diagnostics -> System Activity and during the Speedtest it looks like this:

And so I personally would be looking for newer hardware such the APU2C4 that will do the job for you and
also with higher bandwidth numbers. It comes with three miniPCIe slots and a 4 core CPU w/AES-NI inside
and together with a mSATA you will be able to run more services likes now, as I see it right. It might be
running well also for 100, 200 and perhaps 300 MBit/s at the WAN side. Varia-Store

I have many telecommuters running decade old Acer Aspire One AOA-150 Netbook computers as pfsense routers.

These netbooks have the same processor - Atom N270 (which is a single core but dual thread CPU - as yours and 1GB of RAM, just like yours.

Since Aspire has only one 100 Mb/s ethernet, we configure it to go over inexpensive VLAN enabled 5 port switches.
(And yes we do what everybody says should never be done, yet we have been doing it for years successfully without any incidents)

pfsense 2.3.4-p1 32 bit version runs beautifully and 70/35 lines get driven to their max without any problems.

Neither the CPU nor the RAM gets maxed-out (not even close) while the cable line gets saturated and 100 Mbps could be easily achieved
if we had faster Internet lines for our telecommuters, and especially if we had actual dual ethernets instead of a single etherfast port split
via VLAN configuration.

So, I suspect that you have something not properly setup with your machine. The root cause is probably not the N270.
You might want to dig into the settings and look closely your ethernet port performance.

Maxing out around 70Mbps single core doesn't seem impossible, those were really slow CPUs. It does look like hyperthreading is disabled, so you can see if there's a BIOS setting to enable that. (It also might just not be supported on your motherboard.)

Maxing out around 70Mbps single core doesn't seem impossible, those were really slow CPUs. It does look like hyperthreading is disabled, so you can see if there's a BIOS setting to enable that. (It also might just not be supported on your motherboard.)

You were absolutely right, hyperthreading was disabled. I enabled it and now I have full speed. YEAH! Thank you so much, I never thought about that and probably would have bought new hardware next weekend. And thanks to anybody else for the input.